Caoutchouc mixture for the manufacture of rubber products with low-temperature application capability, resistance to oil, low crystallization tendency and high dynamic stressability

ABSTRACT

The invention relates to a caoutchouc mixture for the manufacture of rubber products with low-temperature application capability, resistance to oil, low crystallization tendency, and high dynamic stressability, on the basis of natural caoutchouc, in particular viscosity-stabilized natural caoutchouc, and the usual mixture ingredients. The essence of said invention lies in that the caoutchouc mixture additionally contains 5 to 30% by weight 1,4-polybutadiene with a high cis-proportion, and 5 to 30% by weight epoxidized natural caoutchouc. An additional mixture variation is introduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a caoutchouc mixture for the manufacture ofrubber products (vulcanizates) with low-temperature applicationcapability even under extreme climatic conditions, resistance to oil,low crystallization tendency and high dynamic stressability, on thebasis of natural caoutchouc and the usual mixing ingredients such asfillers, plasticizers, anti-aging agents, cross-linking agents, zincoxide, as well as additional additives, if necessary.

2. The Prior Art

When passenger cars for long-distance travel are shipped to the formerSoviet Union, operators there request that each second passenger car isequipped with a 32-kw power generator set (power for air-conditioning incold weather). Each of said power generator sets comprises an axlecenter transmission (with two rubber couplings; so-called rubbercentering cone couplings), a universal-joint shaft, a highly elasticrubber preshift coupling, and a generator. The rubber preshift couplingconnects the universal-joint shaft with the generator. The long-distancepassenger cars with the above power generator set and, therefore, alsothe rubber couplings have to be capable of functioning even at outsidetemperatures of -60°. The rubber materials of the coupling shouldcrystallize as little as possible. In addition to such strong influenceof cold, an influence of oil occurs in connection with the rubberpreshift couplings when the car is cleaned, which, however, must not beviewed as permanent. Heretofore, no suitable rubber materials have beenavailable to meet at the same time said requirements with respect tolow-temperature application capability, resistance to oil, lowcrystallization tendency and high dynamic stressability.

In the preparation of a caoutchouc mixture from various types ofelastomer, its compatibility in the polymer blend has to be taken intoaccount. If vulcanizate properties are required which no elastomer alonecan satisfy, it is important that a thermodynamically compatibleelastomer blend is available that optimally possesses all of therequired properties. The use of such a caoutchouc mixture thenrepresents a compromise solution. In addition, such a polymer blend hasto be capable of cross-linking.

Cross-linked caoutchouc mixtures on the basis of natural caoutchouc areknown, whereby reference is made, for example, to the followingliterature sources: U.S. Pat. No.3,342,660; BE-A-698 519; GB-A-2 004286; Chemical Patents Index, Documentation Abstracts Journal (SectionCh, Week 9128, Sep. 11, 1991, Derwent Publications Ltd., London, GB,page 412, AN 91-203 142). However, the caoutchouc mixtures knownheretofore do not satisfy the overall requirements. For example, acaoutchouc mixture is introduced in the last-mentioned document ChemicalPatents Index, which contains epoxidized natural caoutchouc and issuitable for application in the low-temperature range, without, however,satisfying all requirements.

SUMMARY OF THE INVENTION

Now, with the caoutchouc mixture according to the invention, which isbased on natural caoutchouc, in particular viscosity-stabilized naturalcaoutchounc in combination with the additional polymer materialsaccording to the first embodiment (mixture variation I) or the secondembodiment (mixture variation II), a polymer blend is available thatsatisfies the aforementioned requirements or conditions. The additionalpolymer materials can contain from 5 to 30% by weight 1,4-polybutadienewith a high cis-proportion, and from 5 to 30% by weight epoxidizednatural caoutchouc (mixture variation I). Also, the additional polymermaterials can contain from 5 to 20% by weightstyrene-butadiene-caoutchouc and from 5 to 30% by weightethylene-acrylate-caoutchouc (mixture variation II).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Usefully, the following parameters are applied with respect to said twomixture variations:

    ______________________________________                                        Mixture variation I                                                           ______________________________________                                        1,4-polybutadiene                                                             Quantity:            10 to 15% by weight                                      cis-proportion:      >90%                                                     Epoxidized natural caoutchouc                                                 Quantity:            10 to 15% by weight                                      Degree of            about 50%                                                epoxidation:                                                                  ______________________________________                                        Mixture variation II                                                          ______________________________________                                        Styrene-butadiene-caoutchouc                                                                        5 to 10% by weight                                      Quantity:                                                                     Ethylene-acrylate-caoutchouc                                                                       10 to 15% by weight                                      Quantity:                                                                     ______________________________________                                    

The caoutchouc mixtures according to the invention are particularly usedfor the manufacture of shaped articles made of rubber, or of compositearticles made of rubber and metal and/or plastic, in particular ofcouplings for rail vehicle application.

In the caoutchouc mixtures, all percents by weight are based upon thetotal composition weight.

The following experimental part contains formulas (Table 1) and testresults (Table 2), where A represents conventional and B (mixturevariation I) and C (mixture variation II) represent formulas accordingto the invention.

                  TABLE 1                                                         ______________________________________                                        Mixture components (% by wt)                                                                   A         B       C                                          ______________________________________                                        NR CV.sup.a)     44.5      38.0    44.5                                       SBR.sup.b)       6.0       --      5.5                                        BR.sup.c)        13.0      11.0    --                                         ENR.sup.d)       --        14.5    --                                         ACM.sup.e)       --        --      13.5                                       Carbon black N 550.sup.f)                                                                      11.0      11.0    11.0                                       Carbon black N 330.sup.f)                                                                      7.0       7.0     7.0                                        Anti-aging agent 2.0       2.0     2.0                                        Special paraffin.sup.g)                                                                        2.0       2.0     2.0                                        Paraffinic plasticizer                                                                         8.0       8.0     8.0                                        Accelerator      0.6       0.6     0.6                                        Sulphur          1.3       1.3     1.3                                        Inhibitor        0.3       0.3     0.3                                        Zinc oxide       3.0       3.0     3.0                                        Stearic acid     1.3       1.3     1.3                                                         100.00    100.00  100.00                                     ______________________________________                                         .sup.a) Viscositystabilizing natural caoutchouc (Moneyviscosity: about 60     .sup.b) Styrenebutadiene-caoutchouc                                           .sup.c) 1,4polybutadiene with cisproportion above 90%                         .sup.d) 50% expoxidized natural caoutchouc (Weber & Schaer, Hamburg)          .sup.e) Ethyleneacrylate-caoutchoue (Du Pont)                                 .sup.f) Degussa                                                               .sup.g) Hydrierwerke Zeitz                                               

                  TABLE 2                                                         ______________________________________                                        Test results      A        B        C                                         ______________________________________                                        Brittle temp. °C.                                                                        -60      -70      -67                                       Lose factor tan δ at -40° C.                                                       0.078    0.067    0.062                                     Swelling tests                                                                (Soviet transmission oil TSZ9)                                                Storage temperature                                                                             Room temperature                                            Volume swelling after 24 h                                                                      22.60%   6.68%    3.59%                                     Volume swelling after 48 h                                                                      40.12%   10.51%   5.83%                                     Weight swelling after 24 h                                                                      20.88%   7.14%    4.16%                                     Weight swelling after 48 h                                                                      37.21%   10.72%   6.27%                                     Crystallization behavior                                                      (measured on coupling GM 056)                                                 Torsion angle φ.sub.o                                                                       9.3°                                                                            3.3°                                                                            7.4°                               (so-called zero time after 1 day                                              freezing at -25° C.)                                                   Torsion angle φ.sub.14                                                                      7.5°                                                                            2.3°                                                                            5.0°                               (after 14 days freezing at                                                    -25° C.)                                                               Gr.sub.14         1.24     1.44     1.48                                      (stiffness factor; measured as                                                modulus of elasticity in shear                                                for evaluating the crystallization                                            behavior                                                                       ##STR1##                                                                     ______________________________________                                    

Gr₁₄ =1.0 is ideal, i.e., no stiffening at all after 14 days of storageof the coupling at -25° C. However, this is nonexisting in practicallife because all materials (rubber) crystallize more or less during coldstorage. Based on experience, values of up to about 3.0 have to beviewed as a low crystallization behavior. Tests on known couplings,which were classified as "extremely resistant to cold", showed a Gr₁₄-value of about 8, i.e., the coupling is no longer capable offunctioning.

We claim:
 1. Rubber mixture for the manufacture of molded articles madeof rubber, or of composite articles made of rubber and a substanceselected from the group consisting of metal and plastic,comprisingnatural caoutchouc, as well as mixing ingredients selectedfrom the group consisting of fillers, plasticizers, anti-aging agents,cross-linking agents, and zinc oxide, wherein the rubber mixtureadditionally contains 10 to 15% by weight 1,4-polybutadiene with a highcis-proportion of more than 90%, 5 to 30% by weight epoxidized naturalcaoutchouc and wherein all percents by weight are based upon the totalcomposition weight.
 2. Rubber mixture according to claim 1, wherein theepoxidized natural caoutchouc, has had about 50% of its double bondsepoxidized.
 3. Caoutchouc mixture for the manufacture of rubber productscomprisingnatural caoutchouc, as well as mixing ingredients selectedfrom the group consisting of fillers, plasticizers, anti-aging agents,cross-linking agents, and zinc oxide, wherein the caoutchouc mixtureadditionally contains10 to 15% by weight 1,4-polybutadiene with a highcis-proportion of more than 90%, 10 to 15% by weight epoxidized naturalcaoutchouc, and wherein all percents by weight are based upon the totalcomposition weight.
 4. Rubber mixture for the manufacture of moldedarticles made of rubber, or of composite articles made of rubber and asubstance selected from the group consisting of metal and plastic,comprisingnatural caoutchouc, as well as mixing ingredients selectedfrom the group consisting of fillers, plasticizers, anti-aging agents,cross-linking agents, and zinc oxide, wherein the rubber mixtureadditionally contains 5 to 20% by weight styrene-butadiene-caoutchouc,5to 30% by weight ethylene-acrylate-caoutchouc and wherein all percentsby weight are based upon the total composition weight.
 5. Rubber mixtureaccording to claim 4, containing 5 to 10% by weightstyrene-butadiene-caoutchouc.
 6. Rubber mixture according to claim 4,containing 10 to 15% by weight ethylene-acrylate-caoutchouc. 7.Caoutchouc mixture for the manufacture of rubber productscomprisingnatural caoutchouc, as well as mixing ingredients selectedfrom the group consisting of fillers, plasticizers, anti-aging agents,cross-linking agents, and zinc oxide, and wherein the caoutchouc mixtureadditionally contains5to 10% by weight styrene-butadiene-caoutchouc, 10to 15% by weight ethylene-acrylate-caoutchouc, and wherein all percentsby weight are based upon the total composition weight.
 8. Caoutchoucmixture according to claim 3, wherein the epoxidized natural caoutchouchas had about 50% of its double bonds epoxidized.